Revert "webos: Add WEBOS_DISTRO_API_VERSION variable"

This reverts commit 26185faaf078239a4e39d4079acd3482d89f9e31 and
instead, sets the variable in webos.conf . The API version setting
belongs in <distro>.conf proper, i.e. it should not be inheritable.

[GF-2615] Create bitbake variable for webOS API version

Open-webOS-DCO-1.0-Signed-off-by: Herb Kuta <herb.kuta@lge.com>
Change-Id: I85f7783cb897f3786b482a308c52fa5645512cae
Reviewed-on: https://g2g.palm.com/1764
Tested-by: Herb Kuta <herb.kuta@lge.com>
Reviewed-by: Susan Montooth <susan.montooth@lge.com>